Block copolymers are known as polymers comprising molecules in which there is a linear arrangement of blocks, a block being defined as a portion of a polymer molecule in which the monomeric units have at least one constitutional or configurational feature absent from the adjacent portions. In a block copolymer, the distinguishing feature is constitutional, i.e., each of the blocks comprises units derived from a characteristic species of monomer.
A common type of block copolymer is a thermoplastic elastomer. The thermoplastic elastomers in general use contain (i) polymeric blocks (usually referred to as “hard” blocks or A blocks) which (a) are typically amorphous and have a glass transition temperature, Tg,A, which is well above room temperature, or (b) have a crystalline polymer backbone and have a crystalline melting point, Tm,A, which is well above room temperature, and (ii) amorphous polymeric blocks (usually referred to as “soft” blocks or B blocks) which have a glass transition point, Tg,B, which is well below room temperature. Each soft block is linked to at least two hard blocks, so that at temperatures between Tg,B and Tm,A, or Tg,B and Tg,A, the amorphous B blocks are associated with each other, resulting in elastomeric behavior. Above Tm,A or Tg,A, melting or softening of the hard blocks permits viscous flow of the polymeric chains, resulting in thermoplastic behavior. Known thermoplastic elastomers are described for example in U.S. Pat. No. 4,260,659 (Gobran), U.S. Pat. No. 4,361,526 (Allen), U.S. Pat. No. 4,483,978 (Manser), U.S. Pat. No. 4,551,388 (Schlademan), U.S. Pat. No. 4,554,324 (Husman), U.S. Pat. No. 4,656,213 (Schladman), U.S. Pat. No. 4,764,586 (Manser), U.S. Pat. No. 4,778,852 (Futamura), U.S. Pat. No. 4,806,613 (Wardle), U.S. Pat. No. 4,919,737 (Biddle et al), U.S. Pat. No. 4,952,644 (Wardle et al), and U.S. Pat. No. 4,976,794 (Biddle et al). The disclosure of each of those patents and articles is incorporated herein by reference.
However, none of these references has prepared ABA-type block copolymers that are water or alcohol soluble. Water and/or alcohol solubility is an important property for use in commercial applications, particularly consumer applications where water and/or alcohols are considered the safest solvents. In addition, a need exists in the art of thermoplastic elastomers to make these types of polymers more accessible to different types of applications, meaning that the solubility of the polymers needs to be carefully adjusted for particular uses. For example, the water or alcohol solubility of a thermoplastic elastomer for use as a pressure sensitive adhesive will be less that the solubility of a thermoplastic elastomer for use in cosmetic or hair care applications.
In addition, graft type copolymers are generally known. Graft copolymers however, generally differ from ABA block copolymers in that the grafts are not typically attached to a terminal end portion of the middle B block. Also, the control of the architecture and chemical composition of both the backbone and grafts are usually more difficult to achieve in a graft system as compared to a multiblock copolymer.